This invention relates generally to traffic control systems, and more particularly to improvements in monitoring of traffic signal lights for proper operation at controlled roadway intersections.
The present art in the traffic control system uses a controller unit that energizes load switches that drive the signal lamps through a flash transfer relay. In the event that a conflicting signal should arise, a conflict monitor can actuate the relay to transfer the lamp loads to the flasher module.
The conflict monitor measures the traffic signal lamp voltages by converting the AC to DC, enabling a gate which then indicates whether the voltage is present or not. If two signal lamp voltages are ON at the same time in conflicting directions, for instance eastbound and northbound, traffic green signal lights ON, setting up a potential hazard; the conflict monitor will drop or de-energize the flash transfer relay, putting the lamp loads under the control of the flasher, thus putting the intersection into flash.
Prior art has defined a traffic control system as consisting of a traffic controller unit for the purpose of providing 24 volt DC input signals to one or more load switches used to turn traffic signal lamps ON. A conflict monitor device is used to monitor the presence of proper alternating current field wire voltages supplied to power the traffic signal lamps. When improper AC voltages exist, the conflict monitor causes an electro-mechanical relay to transfer, which in turn causes the high current capacity flash transfer relay to remove lamp power from the load switches and to connect the lamp power to a flasher unit, which causes the traffic signal lamps to flash ON and OFF.
In addition to monitoring the AC voltages on the outputs of load switches, the conflict monitor checks for the presence of a 24 volt DC output from the power supplies used by the traffic controller to produce 24 volt DC signals for turning the load switch outputs ON. The 24 volt DC signals supplied from the traffic controller to each of the individual load switch circuits have not previously been monitored within the conflict monitor or the controller unit. A proposed improvement to NEMA traffic control device standards, proposed standard TS2 for future design, would require communication between the traffic controller and the conflict monitor with information sent regarding the programmed traffic controller 24 volt DC signal status, but would not provide a measurement of the 24 volt DC signals actually present at the load switches. U.S. Pat. No. 4,383,240 describes monitoring of DC logic signals, storage, and display of same, along with output status conditions.
There is need for improvements in the control of signal flashing and in the detection and handling of system malfunctions, including that of signal lamps (bulbs), and for simplification of system apparatus and functions.